Vehicle compass system

An electrical compass system for a vehicle, comprising:

• a magnetic field sensor for detecting the earth's magnetic field and for providing electrical signals representative thereof;
• a processing circuit coupled to said sensor for processing said electrical signals from said sensor and for providing heading output signals in response thereto representative of the vehicle heading, said processing circuit including a calibration routine for correcting for heading errors due to vehicle magnetism;
• an indicator circuit coupled to said processing circuit and responsive to said heading output signals for providing an indication of the vehicle heading;
• and
• said processing circuit monitoring said electrical signals from said sensor and reinitializing said calibration routine when said processing circuit determines that the detected signal levels from said sensor have shifted such that said signal levels are outside of a variable threshold, wherein said variable threshold remains unchanged until after each time said processing circuit has completed said calibration routine.

For use in a vehicle compass system having a magnetic field sensor for providing electrical signals representing the earth's magnetic field, a processing circuit for processing said electrical signals and implementing a calibration system for calibrating the compass system to account for changes in vehicular magnetism, and wherein said calibration system is capable of reinitiation which enables the compass system to recover from any change in vehicular magnetism, a method of recovering from a change in vehicular magnetism comprising:

• establishing a variable threshold which encompasses all detected signals levels for each possible vehicle heading for a properly calibrated compass system;
• determining whether the detected signal levels from said sensor have shifted such that said signal levels are outside of said variable threshold;
• and
• reinitiating the calibration system if the detected signal levels are outside of said variable threshold, wherein said processing circuit establishes said variable threshold by establishing threshold limits a distance away from the origin of an origin of a coordinate plane about which the system is calibrated, but is equal to a predetermined multiple of the earth's magnetic field strength.

An electrical compass system for use in a vehicle, said system including a sensor for sensing a magnetic field and for providing electrical signals representative thereof, a processing circuit coupled to said sensor for processing said electrical signals and for providing display output signals in response thereto, and a display circuit coupled to said processing circuit and responsive to said display output signals for displaying the vehicle heading, said processing circuit implementing a calibration system in which said processing circuit continuously monitors said electrical signals from said sensor and determines the maximum and minimum detected signal levels of said electrical signals as the vehicle travels through a 360.degree. loop, said processing circuit generating compensating signals in response to said maximum and minimum detected signal levels for correcting said display output signals to display the correct vehicle heading, said calibration system capable of reinitiation which enables the compass system to recover from any change in vehicular magnetism, wherein the improvement comprises:

• said processing circuit reinitiating said calibration system when said processing circuit determines that the detected signal levels from said sensor have shifted such that said signal levels fall outside of a threshold window which varies as a function of the sensed earth's magnetic field strength and is concentric with a circular plot of the detected signal levels obtained by said calibration system.